I have a Brother HL-5150DN B&W laser with the LT (lower tray option),
and it works extremely well for a duplex printer. The Ethernet is
built-in. Another option would be to purchase the standard HL-5150D,
and look for the Ethernet print server option available for this model.
Sometimes, you can beat the price of the built-in Ethernet version. You
should be in the 400.00 to 450.00 USD price range either way.